1. Field of Invention
This invention relates to a method for making a thin film transistor. In particular, this invention relates to a method for making thin film transistors with lightly doped regions.
2. Related Art
Thin film transistor (TFT) liquid crystal displays (LCD) have been widely used as display devices. As the LCD technology progresses, competition between LCD manufacturers is increasingly keen. To increase the performance of the TFT-LCD, a higher reliability and a cost down of manufacturing the TFT-LCD are the main challenges for TFT manufacturers. The TFT performance is usually improved by modification of its structure and material. The leakage current of the TFT is the main reason of great power consumption. Therefore, it is a critical issue to reduce the leakage current in the TFT. The use of silicon insulation and high-dielectric gate, for example, are well known to obtain a low-leakage TFT. A dual gate structure with a lightly doped intra-gate region has been proposed in the art to achieve the above purpose while further reducing the transversal resistance. This solution has been widely used in the TFT manufacturing field.
A method for making a high-performance TFT includes the steps of exposure, development and etching. For example, a commonly used self-alignment process requires complex etching steps to form a gate. Furthermore, photolithography processes and ion implantations with different dopant concentrations are also required to form heavily doped regions and lightly doped regions in the gate, which complicates the gate manufacture process and thus lowers the throughput.